Base excision repair but not DNA double‐strand break repair is impaired in aged human adipose‐derived stem cells

Abstract

The decline in DNA repair capacity contributes to the age-associated decrease in genome integrity in somatic cells of different species. However, due to the lack of clinical samples and appropriate tools for studying DNA repair, whether and how age-associated changes in DNA repair result in a loss of genome integrity of human adult stem cells remains incompletely characterized. Here, we isolated 20 eyelid adipose-derived stem cell (ADSC) lines from healthy individuals (young: 10 donors with ages ranging 17-25 years; old: 10 donors with ages ranging 50-59 years). Using these cell lines, we systematically compared the efficiency of base excision repair (BER) and two DNA double-strand break (DSB) repair pathways-nonhomologous end joining (NHEJ) and homologous recombination (HR)-between the young and old groups.Surprisingly, we found that the efficiency of BER but not NHEJ or HR is impaired in aged human ADSCs, which is in contrast to previous findings that DSB repair declines with age in human fibroblasts. We also demonstrated that BER efficiency is negatively associated with tail moment, which reflects a loss of genome integrity in human ADSCs. Mechanistic studies indicated that at the protein level XRCC1, but not other BER factors, exhibited age-associated decline. Overexpression of XRCC1 reversed the decline of BER efficiency and genome integrity, indicating that XRCC1 is a potential therapeutic target for stabilizing genomes in aged ADSCs. K E Y W O R D Sadipose-derived stem cells, base excision repair, genome integrity, human aging, XRCC1

Human adipose-derived mesenchymal stromal cells from face and abdomen undergo replicative senescence and loss of genetic integrity after long-term culture

“…In our study, both ASCs shifted from similarly low levels of foci γ-H2AX expression at initial passages to most of the cells pan-expressing it at P12 and progressively thereafter. The γ-H2AX shift from foci to pan expression over passages is a strong indicator of response pathways' activation to persistent DNA damage that ultimately induces cell senescence [46,47]. Interestingly, despite the disparity in cell donors chronological age, no major differences were observed between their genetic stability in vitro, as initially expected.…”

Biomarkers of aging

“…According to the DNA damage theory of aging (Gensler and Bernstein, 1981), DNA lesions are recognized as the primary cause of aging. Supporting this idea, increased DNA damage in senescent cells, progeria cells, and aged individuals have been reported by a great number of studies (d'Adda di Fagagna et al, 2003;Liu et al, 2005;Sedelnikova et al, 2008;Sedelnikova et al, 2004;Wang et al, 2009;Zhang et al, 2020b), making DNA damage a universal biomarker of aging. The frequency of γH2AX foci, a well-known biomarker of double-strand breaks, is upregulated in senescent mouse embryonic fibroblasts and multiple organs, including liver, lung, dermis, crypt of the small intestine, and spleen lymphocytes, in aged mice (Wang et al, 2009).…”

“…Impaired DNA repair is one of the causes of DNA damage accumulation in aged cells, evidenced by reduced expression (Chen et al, 2017;Chen et al, 2020b;Ju et al, 2006;Redwood et al, 2011;Zhang et al, 2020b) or delayed recruitment kinetics of DNA repair factors (Liu et al, 2005;Redwood et al, 2011;Sedelnikova et al, 2008;Zhang et al, 2020b) and a decline in repair fidelity (Li et al, 2016b;Vaidya et al, 2014). Normally, γH2AX foci are cleared upon completion of the repair process.…”

The SIRT6 activator MDL‐800 improves genomic stability and pluripotency of old murine‐derived iPS cells

“…We hypothesized that MDL‐800 promotes genomic stability by boosting DNA repair. Considering SIRT6 participates in repairing both DSBs and DNA damage at bases, we set out to investigate which pathway could be activated post‐MDL‐800 treatment using our previously reported extrachromosomal repair assay (Seluanov, Mao, & Gorbunova, 2010; Zhang et al, 2020). The GFP‐based NHEJ or HR cassettes were linearized by I‐SceI endonuclease in vitro to mimic DSBs.…”

“…Moreover, SIRT6 was reported to regulate BER in both mice and humans (Mostoslavsky et al, 2006; Xu et al, 2015). We then investigated whether MDL‐800 treatment also influences the BER pathway using our previously established plasmid reactivation assay (Xu et al, 2015; Zhang et al, 2020). Briefly, 10 μg pEGFP‐N1 plasmid was mixed with methylene blue, followed by a 120‐min exposure to visible light generated by a 100‐W bulb, which induces 8‐hydroxyguanine damage on plasmids.…”